Like James Bond, the role of Batman is a privilege afforded to only a select few, but the DCEU will soon have three Caped Crusaders actively patrolling Gotham's streets. Robert Pattinson will debut as the newest iteration of Bruce Wayne and his alter-ego in The Batman, while The Flash will be Michael Keaton's first time back as Batman since 1992's Batman Returns. Notwithstanding this, Ben Affleck is still technically the incumbent Dark Knight for the DCEU, and will also return a final time in The Flash.
Batman’s cinematic adventures have been a series of peaks (The Dark Knight), and troughs (Batman and Robin). Notwithstanding this, until now it’s always been the case that there is one movie Batman at a time. Once Christian Bale’s Dark Knight trilogy ended, it was Ben Affleck’s turn, with Batman V Superman: Dawn of Justice. The DCEU’s roadmap for him to star in both future Justice League movies, and at least one solo Batman movie. Affleck's unhappy experience making Justice League, though, along with personal issues, led to him leaving the role early and left Warner Bros. once again without a Batman.
The Flash movie is taking aspects of the Flashpoint storyline in the comics, where Barry Allen travels back in time to prevent his mother's murder, affecting the timeline in the process. In the comics, he encounters an alternate version of Batman (Bruce Wayne's father, Thomas). For The Flash Warner Bros. and DC are taking advantage of their movie library (and capitalizing on the current trend of "requel" moviemaking) by bringing Michael Keaton's Batman back to the screen after 30 years as an older version of the character. Both DC and Marvel are establishing their movie multiverses, where multiple versions of the same character can exist. As is the case with Batman, several comic book superheroes have had their own movies/TV shows over the decades, facilitating a new and instant wave of crossover potential for the DCEU with a built-in audience.
The Flash’s storyline has also enabled Ben Affleck to leave the role on his own terms, allowing the audience to say goodbye to his version of the character, and giving his Batman story a proper end. With Michael Keaton stepping into a mentor/supporting role rather than a principal protagonist, there still needs to be an active Batman fronting his own movies. Affleck's previous stand-alone Batman movie was therefore reimagined by director Matt Reeves into The Batman, with Robert Pattinson taking on Dark Knight duties and giving the DCEU its third Batman. Reeves’ movie is a stand-alone story, and, taking advantage of the multiverse concept, is separate from the DCEU’s primary continuity, being set on Earth-2. Free from the confines of a connected universe, Pattinson’s Batman movies can tell their own stories without the weight of tying into everything else going on around it. Of course, the beauty of the multiverse would also allow for these worlds to collide and disconnect as needed.
Having three Batmans at once wouldn't necessarily have been the original plan for Warner Bros., but as the DCEU experienced teething issues and behind-the-screens problems, the plans changed and evolved over time. Affleck is supposedly done after The Flash, and Pattinson’s Batman is in a different universe on Earth-2. Keaton’s Batman will stick around in the DCEU for now, and following The Flash will next be seen in HBO Max's original movie, Batgirl. Acting as a mentor to Barbara Gordon, her Batgirl may potentially fill the primary DCEU's Caped Crusader role in Affleck's stead.
